So, I went on 14w21b. Thought I'd play around with slimeblocks. But when I placed redstone down, the textures were messed up. It doesn't seem like a problem, but then I tried to turn it on, and these messed up textures are not just the textures, but the redstone itself.
This issue has been reported already. It has been linked to the original bugreport.
Please search before reporting any bugs, as it's likely that one exists already.